It is known to have a plurality of opto-electronic components within a casing, whose components are generally attached thereto in order to produce a particular device or optical unit, such as for use in a photoelectric sensor.
A photoelectric sensor is for example a light barrier, generally known in regard to the safety on the workplace. The barriers generally emit one or more light beams and are usually called light grid or light barrier.
Certain types of light barrier are utilized to detect movement or the intrusion of a foreign body within a zone, such as for example a machinery operating zone, and can guarantee the protection of the operators working with the machinery or other industrial equipment. Other light barriers are constructed in order to control automated industrial processes and are used to verify the assembly process by counting the objects, recognizing the products being transported for example on a conveyor belt, recognizing irregular shapes, etc. Numerous other applications are envisaged.
In general light barriers include two optical units, often called “bars”; one of the two units is the emitter while the other is the receiver. The two optical units can be coupled together; that is to say the same bar can include both the emitter and the receiver. For example, the same optical unit can include light emitters and light receivers.
Light barriers generally utilize emitters that produce either visible spectrum or infrared light sources as the emitter. For example, said sources can include light emitting diodes (LED) mounted at a distance from each other along a transmitter bar that can be placed for example on one side of the monitored zone; photo-transistors, photo-diodes, or other photo-receivers can be used as the receiving elements, which can be mounted for example along a receiver bar on the opposite side of the monitored zone.
In a known example of the operation of a light barrier represented in FIG. 1b, the light sources within the emitter light grid TX emit beams of light towards the photo-receptors of the receiver bar RX. If one or more beams is blocked by an opaque object, such as the arm of an operator (indicated by a circle in FIG. 1b), a control circuit—not illustrated—stops the operating machine that the operator is in charge of, preventing the machine from continuing with the work or otherwise protecting the area and the operator.
As stated above, this interruption can also be utilized to count objects or verify the entrance of goods into a particular zone.
Each light barrier therefore employs a plurality of emitters, as well as a plurality of receivers, and the number of emitters and/or receivers of the plurality depends upon the specific application of the barrier. Emitters and/or receivers are generally assembled together such as to form “arrays” including a number n of emitters and/or receivers spaced apart from the other. The distance between an emitter and a receiver closest to it or between an emitter and receiver closest to it—in other words the pitch of the array—determines the resolution of the light barrier itself.
Each array usually includes a body, commonly molded out of a plastic material, in which n optical chambers are spaced apart and rigidly fixed, within which the optical unit that forms the emitter or receiver is mounted. Additionally these chambers include an opening for the emission or reception of the light signal. These chambers are attached to each other in series side by side such as to form a row of n chambers.
In order to give the desired flexibility as regards the number of emitters and receivers to be used depending upon the type of application, multiple arrays can be combined with each other and then encased within a container or casing that contains, in addition to the arrays, other devices such as an electronic mother board, the power supply, a processing unit, etc. The system of “n” consecutively coupled arrays is always subjected to a compression force produced by the support forces of the container start and end mechanical stops, within which container the arrays are protected: this compression force is variable in that it depends upon the dimensional tolerance of the container itself and the “sum” of the dimensional tolerances of the optical arrays. In other words, the larger the number of arrays coupled together, the greater the dimensional tolerances in play.
It is therefore felt that there is a need to be able to recover the inevitable “play” due to such tolerances. The presence of play in fact causes an incorrect response of the barrier to vibrations or movements, which cause the displacement of one array with respect to the others. Additionally, the presence of play means that the distance between a final optical chamber of an array and an initial optical chamber of the adjacent array are not set apart by a distance that is comparable to the pitch of the optical chambers within a single array. This leads to a change in the resolution of the light barrier. It is in fact desirable that the pitch of consecutive optics be as close as possible to the ideal value that would be obtained if there were not different arrays composing the entire product but rather if it were composed of a single item in order to maintain the degree of resolution equal to the “nominal” resolution value.
In the German patent DE 10 2009 021 645 in the name of Sick AG a light barrier is described comprising at least one array of emitters or receivers. Two receivers or emitters of the array are mutually separated by a flexible separator element.
In the product of the same Applicant referred to as “SG4 extended”, more arrays are mutually coupled together by means of a mechanical coupling and an elastic element is interposed between the casing and the end of the array that it is in contact with it.